/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.graph;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.graph.GraphConstants.DEFAULT_EDGE_COUNT;
import static com.google.common.graph.GraphConstants.DEFAULT_NODE_COUNT;
import static com.google.common.graph.GraphConstants.EDGE_NOT_IN_GRAPH;
import static com.google.common.graph.GraphConstants.NODE_NOT_IN_GRAPH;

import com.google.common.collect.ImmutableSet;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import javax.annotation.Nullable;

/**
 * Configurable implementation of {@link Network} that supports the options supplied by
 * {@link NetworkBuilder}.
 *
 * <p>
 * This class maintains a map of nodes to {@link NetworkConnections}. This class also maintains a
 * map of edges to reference nodes. The reference node is defined to be the edge's source node on
 * directed graphs, and an arbitrary endpoint of the edge on undirected graphs.
 *
 * <p>
 * Collection-returning accessors return unmodifiable views: the view returned will reflect changes
 * to the graph (if the graph is mutable) but may not be modified by the user.
 *
 * <p>
 * The time complexity of all collection-returning accessors is O(1), since views are returned.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @author Omar Darwish
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 */
class ConfigurableNetwork<N, E> extends AbstractNetwork<N, E> {
    private final boolean isDirected;
    private final boolean allowsParallelEdges;
    private final boolean allowsSelfLoops;
    private final ElementOrder<N> nodeOrder;
    private final ElementOrder<E> edgeOrder;

    protected final MapIteratorCache<N, NetworkConnections<N, E>> nodeConnections;

    // We could make this a Map<E, EndpointPair<N>>. It would make incidentNodes(edge) slightly
    // faster, but also make Networks consume 5 to 20+% (increasing with average degree) more
    // memory.
    protected final MapIteratorCache<E, N> edgeToReferenceNode; // referenceNode == source if
                                                                // directed

    /** Constructs a graph with the properties specified in {@code builder}. */
    ConfigurableNetwork(NetworkBuilder<? super N, ? super E> builder) {
        this(builder,
                builder.nodeOrder
                        .<N, NetworkConnections<N, E>>createMap(builder.expectedNodeCount.or(DEFAULT_NODE_COUNT)),
                builder.edgeOrder.<E, N>createMap(builder.expectedEdgeCount.or(DEFAULT_EDGE_COUNT)));
    }

    /**
     * Constructs a graph with the properties specified in {@code builder}, initialized with the
     * given node and edge maps.
     */
    ConfigurableNetwork(NetworkBuilder<? super N, ? super E> builder, Map<N, NetworkConnections<N, E>> nodeConnections,
            Map<E, N> edgeToReferenceNode) {
        this.isDirected = builder.directed;
        this.allowsParallelEdges = builder.allowsParallelEdges;
        this.allowsSelfLoops = builder.allowsSelfLoops;
        this.nodeOrder = builder.nodeOrder.cast();
        this.edgeOrder = builder.edgeOrder.cast();
        // Prefer the heavier "MapRetrievalCache" for nodes if lookup is expensive. This optimizes
        // methods that access the same node(s) repeatedly, such as Graphs.removeEdgesConnecting().
        this.nodeConnections = (nodeConnections instanceof TreeMap)
                ? new MapRetrievalCache<N, NetworkConnections<N, E>>(nodeConnections)
                : new MapIteratorCache<N, NetworkConnections<N, E>>(nodeConnections);
        this.edgeToReferenceNode = new MapIteratorCache<E, N>(edgeToReferenceNode);
    }

    @Override
    public Set<N> nodes() {
        return nodeConnections.unmodifiableKeySet();
    }

    @Override
    public Set<E> edges() {
        return edgeToReferenceNode.unmodifiableKeySet();
    }

    @Override
    public boolean isDirected() {
        return isDirected;
    }

    @Override
    public boolean allowsParallelEdges() {
        return allowsParallelEdges;
    }

    @Override
    public boolean allowsSelfLoops() {
        return allowsSelfLoops;
    }

    @Override
    public ElementOrder<N> nodeOrder() {
        return nodeOrder;
    }

    @Override
    public ElementOrder<E> edgeOrder() {
        return edgeOrder;
    }

    @Override
    public Set<E> incidentEdges(Object node) {
        return checkedConnections(node).incidentEdges();
    }

    @Override
    public EndpointPair<N> incidentNodes(Object edge) {
        N nodeU = checkedReferenceNode(edge);
        N nodeV = nodeConnections.get(nodeU).oppositeNode(edge);
        return EndpointPair.of(this, nodeU, nodeV);
    }

    @Override
    public Set<N> adjacentNodes(Object node) {
        return checkedConnections(node).adjacentNodes();
    }

    @Override
    public Set<E> edgesConnecting(Object nodeU, Object nodeV) {
        NetworkConnections<N, E> connectionsU = checkedConnections(nodeU);
        if (!allowsSelfLoops && nodeU == nodeV) { // just an optimization, only check reference
                                                  // equality
            return ImmutableSet.of();
        }
        checkArgument(containsNode(nodeV), NODE_NOT_IN_GRAPH, nodeV);
        return connectionsU.edgesConnecting(nodeV);
    }

    @Override
    public Set<E> inEdges(Object node) {
        return checkedConnections(node).inEdges();
    }

    @Override
    public Set<E> outEdges(Object node) {
        return checkedConnections(node).outEdges();
    }

    @Override
    public Set<N> predecessors(Object node) {
        return checkedConnections(node).predecessors();
    }

    @Override
    public Set<N> successors(Object node) {
        return checkedConnections(node).successors();
    }

    protected final NetworkConnections<N, E> checkedConnections(Object node) {
        NetworkConnections<N, E> connections = nodeConnections.get(node);
        if (connections == null) {
            checkNotNull(node);
            throw new IllegalArgumentException(String.format(NODE_NOT_IN_GRAPH, node));
        }
        return connections;
    }

    protected final N checkedReferenceNode(Object edge) {
        N referenceNode = edgeToReferenceNode.get(edge);
        if (referenceNode == null) {
            checkNotNull(edge);
            throw new IllegalArgumentException(String.format(EDGE_NOT_IN_GRAPH, edge));
        }
        return referenceNode;
    }

    protected final boolean containsNode(@Nullable Object node) {
        return nodeConnections.containsKey(node);
    }

    protected final boolean containsEdge(@Nullable Object edge) {
        return edgeToReferenceNode.containsKey(edge);
    }
}
